
ML66517 Family User’s Manual
Chapter 8
General-Purpose 8/16 Bit Timers
8 – 27
8.7.2 Description of Timer 4 Registers
(1) General-purpose 8-bit timer 4 counter (TM4C)
The general-purpose 8-bit timer 4 counter (TM4C) is an 8-bit up-counter. When this counter overflows, an
interrupt request is generated and it is loaded with the contents of general-purpose 8-bit timer 4 register
(TM4R). TM4C can also be used as a baud rate generator for SIO1.
TM4C can be read from and written to by the program.
When reset (
RES signal input, execution of a BRK instruction, overflow of the watchdog timer, opcode
trap), the contents of TM4C are undefined.
[Note]
Writing a timer value to TM4C causes the same value to also be written to the general-purpose 8-bit timer 4
register (TM4R).
(2) General-purpose 8-bit timer 4 register (TM4R)
The general-purpose 8-bit timer 4 register (TM4R) consists of 8 bits. This register stores the value to be
reloaded into the general-purpose 8-bit timer 4 counter (TM4C).
TM4R can be read from and written to by the program.
When reset (
RES signal input, execution of a BRK instruction, overflow of the watchdog timer, opcode
trap), the contents of TM4R are undefined.
(3) General-purpose 8-bit timer 4 control register (TM4CON)
The general-purpose 8-bit timer 4 control register (TM4CON) consists of 5 bits.
Bits 0 to 2 (TM4C0 to
TM4C2) of TM4CON select the timer 4 count clock and bit 3 (TM4RUN) specifies to start or halt the
counting. Bit 7 (TM4OUT) is set to the initial level (High or Low) at start-up.
And each time TM4C
overflows, the content of bit 7 (TM4OUT) is reversed.
TM4CON can be read from and written to by the program. However, write operations are invalid for bits 4
to 6. If read, a value of “1” will always be obtained for bits 4 to 6.
When reset (
RES signal input, execution of a BRK instruction, overflow of the watchdog timer, opcode
trap), TM4CON becomes 70H.
Figure 8-14 shows the TM4CON configuration.
[Note]
Just before TM4C overflows, if an SB, RB, XORB or other read-modify-write instruction is performed on
TM4CON, then TM4OUT may not operate correctly.